Antimicrobial resistance patterns of Streptococcus uberis isolates recovered from bovine mastitis

Öz

Streptococcus uberis, which is a major cause of bovine mastitis in the dairy industry, is commonly treated with antimicrobials. The objective of this study was to investigate antimicrobial resistance (AMR) patterns of S. uberis isolates recovered from bovine mastitis. Totally 120 milk samples were collected in 2025 from cows with mastitis on a farm. S. uberis isolates were identified using standard bacteriological analyses and confirmed by sequence analysis of the 16S rRNA gene. Six different antimicrobials (gentamicin, streptomycin, penicillin, vancomycin, erythromycin, and tetracycline) were used for AMR test by the Kirby-Bauer disc diffusion method. Eighteen S. uberis isolates (15.0%, 18/120) were recovered, none of which were susceptible to all the tested antimicrobials. All isolates (100.0%, 18/18) were resistant to aminoglycosides, gentamycin, and streptomycin. In contrast, all isolates (100.0%, 18/18) were susceptible to penicillin and vancomycin. This finding supports the use of beta lactams as first-line antimicrobials to treat S. uberis infections. Additionally, 27.8% (5/18) and 61.1% (11/18) of the isolates were resistant to erythromycin and tetracycline, respectively. The high resistance rate for tetracycline indicates that it is not an effective treatment option for S. uberis infections. Four different AMR patterns were determined. Isolates with the CN-S-E-TE pattern were defined as multidrug-resistant (MDR) (16.7%, 3/18). The identification of MDR isolates emphasizes the necessity of conducting AMR testing prior to initiating antimicrobial treatment for bovine mastitis. In conclusion, these findings align with existing literature and demonstrate the significance of regular surveillance to guide evidence-based and sustainable approaches in bovine mastitis management.

Anahtar Kelimeler

• Bovine mastitis
• Monitoring AMR
• Penicillin
• Streptococcus uberis
• Tetracycline

Sığır mastitinden izole edilen Streptococcus uberis suşlarının antimikrobiyal direnç profilleri

Öz

Süt sığırı yetiştiriciliğinde sığır mastitisinin başlıca etkenlerinden biri olan Streptococcus uberis, genellikle antimikrobiyal ajanlarla tedavi edilmektedir. Bu çalışmanın amacı, mastitisli sığırlardan izole edilen S. uberis suşlarının antimikrobiyal direnç (AMR) profillerini araştırmaktı. Bu amaçla, 2025 yılında bir çiftlikteki mastitisli ineklerden toplam 120 adet süt numunesi toplandı. S. uberis izolatları, standart bakteriyolojik yöntemler ile tanımlandı ve 16S rRNA geni dizi analizi ile doğrulandı. Kirby-Bauer disk difüzyon yöntemi ile gerçekleştirilen AMR testi için altı farklı antimikrobiyal ajan (gentamisin, streptomisin, penisilin, vankomisin, eritromisin ve tetrasiklin) kullanıldı. Toplam 18 adet S. uberis izolatı (%15,0, 18/120) elde edildi ve test edilen antimikrobiyallerin tamamına duyarlı izolat bulunmadı. Tüm izolatlar (%100,0, 18/18), aminoglikozitler olan gentamisin ve streptomisine dirençli bulundu. Buna karşılık, tüm izolatlar (%100,0, 18/18) penisilin ve vankomisine duyarlı bulundu. Bu bulgu, S. uberis enfeksiyonlarının tedavisinde beta laktamların birinci basamak antimikrobiyaller olarak kullanılmasını desteklemektedir. Ayrıca izolatların %27,8’i (5/18) eritromisine ve %61,1’i (11/18) tetrasikline dirençli bulundu. Tetrasikline karşı saptanan yüksek direnç oranı, bu antimikrobiyalin S. uberis enfeksiyonları tedavisinde etkili bir seçenek olmadığını göstermektedir. Dört farklı AMR profili saptandı. CN-S-E-TE (gentamisin, streptomisin, eritromisin, tetrasiklin) direnç profiline sahip izolatlar çoklu ilaç dirençli (MDR) izolatlar (%16,7, 3/18) olarak tanımlandı. MDR izolatlarının varlığı, sığır mastitisinin tedavisine başlanmadan önce AMR testlerinin yapılmasının gerekliliğini vurgulamaktadır. Sonuç olarak, bu bulgular mevcut literatür ile uyumludur ve sığır mastitisinin yönetiminde kanıta dayalı ve sürdürülebilir yaklaşımları yönlendirmek amacıyla düzenli izleme çalışmalarının önemini ortaya koymaktadır.

Anahtar Kelimeler

• Antimikrobiyal direnç izleme
• Penisilin
• Sığır mastiti
• Streptococcus uberis
• Tetrasiklin

Kaynakça

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